The invention relates to a charged particle lithography system with a sensor assembly.
Such a lithography system is for example disclosed in the International Patent Application WO2007/032670. The lithography systems disclosed in this International Patent Application is arranged for transferring a pattern onto the surface of a target, using a charged particle optical unit for generating a plurality of charged particle beams, modulating said charged particle beams, and directing said charged particle beams towards the surface of the target. The charged particle beams are scanned in one or more directions over the surface of the target, and during said scanning each charged particle beam writes a part of said pattern on said surface of the target.
In order to write a high-resolution pattern on a target, for example a wafer or a mask, the position of each beam at or near the surface to be exposed must preferably be known within a distance of a few nanometers. In order to determine the characteristics of a charged particle beam, and in particular of said plurality of charged particle beams, a sensor is used which is combined with a converter element for converting charged particle beams into a light beams. Said sensor comprises an array of light sensitive detectors located in line with said converter element for detecting said light beams. Preferably the converter element is provided with a blocking element which comprises sharp edges. The converter element, in particular the blocking element thereof, is arranged substantially at the same level as the surface of the target. By scanning a charged particle beam over the converter element in a direction substantially perpendicular to the sharp edges and monitoring the change of light intensity of the light beam corresponding to the charged particle beam, the position and diameter of the charged particle beam can be established.
As disclosed in WO2007/032670 the converter element is arranged directly above the array of light sensitive detectors, which provides a very compact assembly. The array of light sensitive detectors is provided with cabling for communicating the measured data to a control device comprising a processor for processing the measured data to determine the characteristics of a charged particle beam.
In order to position the blocking element substantially at the same level as the surface of the target, the assembly of sensor and converter element is arranged in or adjacent to the target holder. Preferably the assembly is integrated in the target holder.
The target holder is arranged on top of an assembly of stages for accurately moving the target with respect to the charged particle optical unit, and is arranged inside a vacuum chamber. A disadvantage of the integration of the assembly in the target holder inside the vacuum chamber, is that the assembly arranged on top of the assembly of stages must be connected to the control device outside the vacuum chamber, without hindering the accurate moving of the target.
It is an object of the present invention to provide a more convenient positioning of the sensor.